"How can it be that something for $690 sounds better than ML's and Krells "
Just because an inexpensive item has a better Audioreview then a Krell/Levinson/Rowland/etc does not mean it is better ... it just means a LOT of people have bought them and really like them. Same with Odessey, Newform, and others.
How many of the people who bought an ELAD could afford a top-of-the line Levinson/Rowland/Audio Research/etc pre-amp ... not many !
I myself have auditioned several > $4K pre-amps and each has is unique sound. I also have had an inexpensive Placette passive, and EVS attenuators, and loved them too. I also bought some Newform's for a second system, and have brought them to a new level with some capacitor upgrades.
A home audition is the only way to know what works for you, your system, and your room, and your significant other !